Twins Cold Piping Size? 3.5" or 4"

[jkretzer]

what is everyones thoughts on size for the cold piping 3.5" or 4"? i have heard both sides that each one is better. trying to get some feedback. josh

 

[Diesel Freak]

really does not matter.

the pressure drop on a 3" pipe from a normally sized primary (s400, GT42...etc...) is negligeable

3" pipe has a pressure drop of 0.686 psig

4" pipe has a pressure drop of 0.215 psig

This is at a flow rate of 90 pounds per minute.

basicly what I am saying, 3.5 or 4 it does not matter. I am using a 3.5 incher. This welds perfectly to the 3.5" GT42 outlet flange that ATP sells...the same part also fits the S400.

http://www.atpturbo.com/Merchant2/m...tp&Product_Code=ATP-FLS-055&Category_Code=BCS

Hot pipe diameter is more critical than cold pipe diameter. The pipe should be no larger than the exducer of the secondary turbine. This keeps gass expansion to a minimum between the turbine stages. Dumping exhaust gases from a small turbine like a HX40 or any s400 into a 4" pipe that connects to a T6 flanged primary just makes no sence. This makes the exhaust gases slow down and then speed back up as it enters the primary scroll...this WASTES energy.

The main restriction is the primary housing, not the hot pipe. Keeping the gases in the hot pipe mooving fast will help spool, and make the system more efficient.

 

[Signature600]

really does not matter.

the pressure drop on a 3" pipe from a normally sized primary (s400, GT42...etc...) is negligeable

3" pipe has a pressure drop of 0.686 psig

4" pipe has a pressure drop of 0.215 psig

This is at a flow rate of 90 pounds per minute.

basicly what I am saying, 3.5 or 4 it does not matter. I am using a 3.5 incher. This welds perfectly to the 3.5" GT42 outlet flange that ATP sells...the same part also fits the S400.

http://www.atpturbo.com/Merchant2/m...tp&Product_Code=ATP-FLS-055&Category_Code=BCS

Hot pipe diameter is more critical than cold pipe diameter. The pipe should be no larger than the exducer of the secondary turbine. This keeps gass expansion to a minimum between the turbine stages. Dumping exhaust gases from a small turbine like a HX40 or any s400 into a 4" pipe that connects to a T6 flanged primary just makes no sence. This makes the exhaust gases slow down and then speed back up as it enters the primary scroll...this WASTES energy.

The main restriction is the primary housing, not the hot pipe. Keeping the gases in the hot pipe mooving fast will help spool, and make the system more efficient.

Great info...I was gonna use 3.5" for ease of installation, and still might...but man, that 4" just looks better!

BUT, I will be using 3" for the hot-pipe now...I wasn't sure before.

Thanks for the explanation that I thought I knew :hehe:
Chris

 

[oil-burner]

Hot pipe diameter is more critical than cold pipe diameter. The pipe should be no larger than the exducer of the secondary turbine. This keeps gass expansion to a minimum between the turbine stages. Dumping exhaust gases from a small turbine like a HX40 or any s400 into a 4" pipe that connects to a T6 flanged primary just makes no sence. This makes the exhaust gases slow down and then speed back up as it enters the primary scroll...this WASTES energy.

QUOTE]

From what I got from that then 4" or bigger exhaust is a waste also.

scot

 

[Scooter's Roofing]

Hot pipe diameter is more critical than cold pipe diameter. The pipe should be no larger than the exducer of the secondary turbine. This keeps gass expansion to a minimum between the turbine stages. Dumping exhaust gases from a small turbine like a HX40 or any s400 into a 4" pipe that connects to a T6 flanged primary just makes no sence. This makes the exhaust gases slow down and then speed back up as it enters the primary scroll...this WASTES energy.

QUOTE]

From what I got from that then 4" or bigger exhaust is a waste also.

scot

you missed the point... keep the heat energy in the exhaust so that it can feed the bottom turbo. once you've got no more turbos to light, free it up!

 

[thojer81]

so in other words in my case i'm using a hx35/k31, i could use 3'' on the hot pipe and 4'' on the cold side or am i wrong on this.$.02

 

[justinp20012500]

From what I got from that then 4" or bigger exhaust is a waste also.

scot

It does not matter what the exhaust gas does after it leaves the last turbo. Gas expansion will actually help scavenging.

 

[smokeisfun]

i have 3" on my cold pipeing...why go bigger...everything else is only 3"...(air-air inlet and outlet)